Dynamic capacity allocation in optical communication networks

ABSTRACT

Techniques for efficiently utilize the available bandwidth in a communication network are described. One example implementation includes a method of optical communication including receiving bandwidth requests from multiple network devices in an optical network, receiving communication capability information about the multiple network devices, generating a transmission schedule that specifies transmissions in the optical network in multiple time slots with a corresponding modulation format, and transmitting and/or receiving data based on the transmission schedule.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent document claims the benefit of priority of U.S. ProvisionalPatent Application No. 62/503,929, filed on May 9, 2017. The entirecontent of the before-mentioned patent application is incorporated byreference as part of the disclosure of this document.

TECHNICAL FIELD

This patent document relates to digital communication, and, in oneaspect, optical communication systems.

BACKGROUND

There is an ever-growing demand for data communications in applicationareas such as wireless communications, fiber optic communications and soon. The demand on access networks is especially growing because not onlyare user devices such as smartphones and computers using more and morebandwidth due to multimedia applications, but also the total number ofdevices for which data is carried over the access networks isincreasing. For profitability and to meet increasing demand, equipmentmanufacturers and network operators are continually looking for ways inwhich operational and capital expenditure can be reduced.

SUMMARY

The present document discloses techniques for dynamic bandwidthallocation in a communication system.

In one example aspect, a method of optical communication is disclosed.The method includes receiving bandwidth requests from multiple networkdevices in an optical network, receiving communication capabilityinformation about the multiple network devices, generating atransmission schedule that specifies transmissions in the opticalnetwork in multiple time slots with a corresponding modulation format,and transmitting and/or receiving data based on the transmissionschedule.

In another example aspect, an optical communication apparatus isdisclosed. The apparatus includes a processor that is configured toreceive bandwidth requests from multiple network devices in an opticalnetwork, a receiver configured to receive communication capabilityinformation of the multiple network devices, a scheduler configured togenerate a transmission schedule that specifies transmissions in theoptical network in multiple time slots with a corresponding modulationformat, and an elastic transceiver configure to transmit and/or receivedata based on the transmission schedule.

In yet another example aspect, a method of wireless communication isdisclosed. The method includes transmitting bandwidth requests to acontroller in an optical network, providing communication capabilityinformation to the controller, receiving a transmission schedule thatspecifies transmissions in the optical network in multiple time slotswith a corresponding modulation format, and transmitting and/orreceiving data based on the transmission schedule.

These, and other aspects, are disclosed in the present document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example passive optical network.

FIG. 2 is a block diagram depicting an example embodiment of atwo-dimensional dynamic bandwidth allocation scheme.

FIG. 3 is a flowchart representation of an example method of dynamicupstream and downstream bandwidth allocation.

FIG. 4 is a block diagram of an example implementation of a downstreambandwidth allocation technique.

FIG. 5 is a block diagram of an example implementation of an upstreambandwidth allocation technique.

FIG. 6 is a flowchart for an example method of optical communication.

FIG. 7 is a block diagram of an example implementation of an opticaltransmission apparatus.

FIG. 8 shows an example of an optical communications apparatus.

DETAILED DESCRIPTION

As optical access networks continue to evolve to a more heterogeneoustype of network supporting both fixed (FTTx) and wireless (mobilebackhaul and fronthaul) services, it is expected that many differentsystems will coexist on the same passive optical network (PON). Thesesystems and the devices operating in these systems often arecommunicating using different data rates which may change depending onthe time of data and other operational conditions. It is, therefore,useful for an optical communication network to be able to quicklyreconfigure the capacity for different systems with users at differentlocations.

In a traditional PON system, such situations are handled by varioustechniques, collectively called dynamic bandwidth allocation (DBA)mechanisms. However, traditional PON bandwidth allocation is based onallocation of capacity in a time-division multiplexed (TDM) manner.Using such schemes, different devices are allocated differenttransmission time durations and slots in sharing a communicationbandwidth with each other. However, such bandwidth sharing based on timeis limited in a heterogeneous network.

The techniques described in the present document can be used by variousembodiments to provide an elastic capacity/bandwidth allocation method.Some embodiments may intelligently allocate capacity or bandwidth bydynamically configuring both time and modulation formats (e.g., morebits per symbol for higher spectral efficiency) of the transmittedsignals. In some embodiments, such a method may be used for meeting thecapacity demand for end users at widely distributed geographiclocations.

Section headings are used in the present document to improve readabilityand do not limit the disclosed technology and embodiments to therespective sections.

For highlighting some aspects of bandwidth allocation, the followingfour use cases are used:

In a first use case, a location dependent data rate is provided wherethe network may provide a high aggregated capacity in urban area and arelatively lower aggregated capacity in rural areas where the number ofusers, and thus the amount of optical equipment, may be fewer and may besparsely distributed.

In a second use case, a service dependent data rate provides backhaulingor front hauling of multiple generations of wireless networks (3G, 4G,and/or 5G). The network allocates capacity based on the different systemrequirements.

In a third use case, an on-demand capacity allocation refers to networkbandwidth that may be made available for special occasions such as majorsports events, large concerts, political demonstrations, etc. To meetsuch a bandwidth demand, the network may be reconfigured to support thecapacity increase in the duration of the events. This change inbandwidth allocation may be pre-planned or on demand.

In a fourth use case, small cells may be formed and taken down by userson an ad-hoc basis. Therefore, such a bandwidth allocation may becharacterized by fast provisioning of high number of end users; each hasdifferent data rate requirements.

It is envisioned that in a heterogeneous network, not only do differentusers need different data rates (second use case), but the same user mayhave dynamic data rate requirements (first, third, and fourth usecases). The optical line terminal (OLT) at the central office (CO) canchange the modulation format to achieve different data rates. Asreceiver sensitivity depends on modulation format used, the exact datarate a user (at the Optical Network Unit, ONU) can receive will dependon its distance to the OLT.

Examples of Upstream and Downstream Embodiments

This section provides some examples of the transceiver technology thatcan be used to implement the elastic bandwidth allocation mechanismdescribed in this document.

In some embodiments, a transceiver may be flexibly sending mixedmodulation formats (NRZ, Duobinary, PAMn, mQAM) or data rates (1 G, 25G, 50 G, 100 G, or other rates) depending on ONUs' locations andcapacity use.

For example, in some embodiments, in the downstream (DS) direction, eachTDM frame may be transmitted using its own modulation format and symbolrate such that the modulation format and symbol rate used in one timeslot may change from those used in a next time slot. For compatibility,some embodiments of OLTs may be able to communicate with both legacyONUs and elastic ONUs at the same time.

Within a TDM frame, a transmission may include multiple symbols. Eachsymbol may contain different modulation format such as PAM-2, PAM-4,PAM-8, PAM-16, QPSK, 4-QAM, 8-QAM, 16 QAM, 32, QAM, 64, QAM, etc. An ONUmay have a receiver (or transmitter) that is flexible or elastic to beable to receive (or transmit) differing modulation formats.

In the upstream (US) direction, an OLT receiver implementation maydetect bursts from both legacy and elastic ONUs. An ONU burst header mayinclude an identifier to tell the OLT about the modulation format beingused by that transmission. Such OLT receivers may implement DigitalSignal Processing (DSP) and equalize input signals from ONUs withdifferent modulation formats and symbol rates.

The transmission and reception may be performed according to a dynamicbandwidth allocation algorithm implementation, as described in thepresent document.

Examples of supported combinations of data rates and modulation formatsusing a single wavelength include 1 G NRZ (non-return to zero), 10 GNRZ, and 25 G NRZ. Additional examples include 25 G rate using newmodulation formats, e.g., 25 G PAM4 (12.5 G symbol rate) or 25 G 16 QAM(12.5 G symbol rate); 50 G new modulation formats; 50 G PAM4 (25 symbolrate); 50 G 16 QAM (25 G symbol rate); 50 G 64 QAM (8.33 G symbol rate);and 100 G new modulation formats; 100 G PAM4 (50 G symbol rate); 100 GPAM16 (25 G symbol rate); and 100 G 64 QAM (50 G symbol rate).

In some embodiments, the bandwidth allocation procedures may be managedby a network coordinator, e.g., a software-defined network (SDN)orchestrator that is located in Cloud. In one aspect, the dynamicallyprovisioned available bandwidth to different users is treated as a twodimensional resource (time as one dimension and bits per symbol as theother dimension), compared with legacy systems with only time as theresource. In another aspect, the disclosed embodiments can use all ofthe available bandwidth. For example, for communication with ONUs withlower path loss and/or more sensitive receivers, the bandwidthallocation procedure may allocate higher-level modulation formats toincrease the total capacity.

FIG. 1 shows an example of a conventional TDD optical network. For sucha legacy PON, e.g., GPON, EPON, XG(S)-PON, and NG-PON2, with NRZ-OOKmodulation format, time resource is the only dimension for DBA for bothdownstream (DS) and upstream (US) directions. By changing the allocatedtime window for each ONU, the centralized OLT can dynamically change theDS/US bandwidth among different ONUs. This is depicted based on thewidth of the data package along the horizontal (time) axis. For example,in the depicted allocation, DS bandwidth to ONU 3 is the largest,followed by DS bandwidth allocated to ONU 2, followed by equal bandwidthallocated to ONUs 1 and 4.

In some embodiments of PON systems using advanced modulation formats,e.g., PAM-4/8/16 and DMT/QAM-4/8/16/32/64, there is a possibility ofcoexistence of signals using these modulation formats with basic NRZ-OOKsignals. In general, advanced modulation formats require higher receivedoptical power. ONUs at a shorter distance to OLT experiences lower pathloss, thus higher received power. As such, these ONUs can support higherlevel modulation formats with higher spectral efficiency. Otheroperational factors may also influence the highest level modulation thatcan be achieved between an OLT and an ONU. These include quality of theoptical transmission medium, technology used in implementing the OLT andthe ONU, and so on.

In a system with flexible modulation formats, an ONU may be capable ofsending mixed modulation formats (NRZ, Duobinary, PAMn, or mQAM)depending on its location (path loss). The OLT may collect all theinformation about each ONU, including the path loss, maximum bits persymbol supported, and both US/DS bandwidth demands. It can then create atwo-dimensional bandwidth map (BW map) for each ONU based on theinformation collected.

FIG. 2 shows an example optical network 200 of elastic OLT/ONUs withflexible modulation formats. In such a system, the OLT 206 candynamically change the bandwidth of each ONU in two dimensions—time andthe number of bits per symbol. A controller 204, either co-located withthe OLT, or somewhere else in the network, may be used to perform atleast some of the bandwidth allocation functions as described herein.The distances between ONUn (where n=1, 2, 3, . . . ) and the OLT havethe relationship of D1<D2<D3<D4 and ONUn supports 4, 3, 2, or 1 bit(s)per symbol, respectively. In this way, the bandwidth allocation schemecan be realized in two dimensions—time slots and bits per symbol. Avisual depiction is shown in graph 202. The total area occupied by therectangles 1, 2, 3, and 4 is indicative of total number of bitstransmitted in the optical network 200. Furthermore, area of eachrectangle 1 to 4 is approximately proportional to the bandwidth of thecommunication with the corresponding ONU. As can be seen, communicationwith ONU1 occurs at the highest number of bits per symbol and with acorresponding time slot allocated for transmission to ONU1 that isshorter than the other time slots. However, the number of bitscommunicated during the time slot for ONU1 may be more than time slots2, 3 or 4 because the number of bits per symbol increases the number ofbits communicated more than the smaller time slot reduces the number ofbits communicated.

FIG. 3 shows an example of a BW map creation and an updating process 300for both DS and US. For DS, the OLT sends data to different ONUs,depending on the demand, the time resource, and the supported bits persymbol. For US, the elastic DBA (eDBA) function provides input to theOLT US scheduler, which is also responsible for generating the BW maps.The process 300 may include operation 302 in which each ONU registerswith the network, reports the path loss being seen by the ONU andfurther reports the maximum modulation format that the ONU can support.Using this information, at operation 304, the OLT updates a localbandwidth map for US and DS data transmissions in the network.

From time to time, the OLT may update (308) DS bandwidth map. When theupdate is performed, the OLT may use the updated bandwidth map forscheduling (314) further DS transmissions in the network. This may beperformed by scheduling (318) time slots and bits per symbol accordingto bandwidth need. Further, when an ONU decides (306) that it has a needfor additional bandwidth, and issues the demand to the OLT, the OLT mayperform another update (308) to the downstream map.

For US data transmissions, a bandwidth map update may be performed at310. This operation may be triggered by a demand from an ONU foradditional US bandwidth. Based on the request, a transmission schedulermay schedule (316) US transmissions based on time slot width and themodulation format to meet the bandwidth requirement of each device(320).

Different algorithms can be used for bandwidth allocation including forthe US DBA. FIGS. 4 and 5 depict creation of a BW map for DS and US. TheOLT stores the BW maps and updates them during registration and throughrequests from ONUs. For DS, the OLT sends the data to different ONUs byscheduling the time slots and modulation formats. For US, the eDBAfunction then provides input to the OLT US scheduler as an Alloc_ID,which specifies the timing (considering the guard time between bursts),duration length and the bits per symbol of the upstream transmissionfrom the ONUs.

FIG. 4 depicts an optical network 400 in which the OLT 402 includes ascheduler 404 and an elastic transmitter 406. The scheduler 404 uses alocally stored bandwidth allocation map 408 that the scheduler 404 usesto dynamically allocate downstream bandwidth to multiple ONUs 412. Theelastic transmitter 406 performs data modulation according to themodulation format and time slot duration specified by the scheduler 404.Accordingly, the elastic transmitter 406 can elastically and dynamicallychange the modulation format and constellation density of the DS signal,possibly on a symbol by symbol basis. The optical transmitter 410converts electrical signals into modulated optical signals using anelectrical to optical conversion technology.

In some embodiments, the scheduler 404 may allocate bandwidth based oncurrent requests from an ONU such that the allocated bandwidth meets thedemand over a number of transmission maps. For example, for the sake ofillustration, it is assumed that the rectangle allocated to ONUi at 4bits/symbol represents 200 bits of data being transmitted during thetime slot (50 symbols×4 bits/symbol). For the sake of illustration, ifit is assumed that bandwidth requirement of ONUi changes from 200 bitsper transmission frame to 240 bits per transmission frame. The schedulermay be able to accommodate the increased bandwidth requirement byscheduling longer time slots (60 symbols×4 bits/symbol). However, insome cases, the scheduler may not be able to increase the time allocatedto ONUi due to other competing demands on the bandwidth (e.g., by otherONUs). In such a case, the scheduler may provide bandwidth allocation toONUi which is “on the average” 240 bits per transmission frame. This maybe accomplished by providing opportunistically different bandwidth overmultiple transmission frames such that the average is about 240 bits pertransmission frames. For example, over five transmission frames, theallocated bandwidth may be 200 bits, 300 bits, 300 bits, 200 bits, 200bits, averaging to 240 bits. Furthermore, when averaging over multipletransmission frames, the number of transmission frames over which atarget average bitrate is achieved may depend on the latency toleranceof the corresponding ONU. For example, an ONU that is able to toleraterelatively higher data latency may be allocated bandwidth by averagingover a greater number of transmission maps.

In some embodiments, the scheduler may perform the optimization byassociating implicit or explicit priorities with the bandwidth requestsfrom various ONUs. The priority may be based on a priority field in thebandwidth request, or may be based on another rule such as round robinallocation, and so on.

FIG. 5 depicts an optical network 500 in which dynamic scheduling isused for US data transmissions received at the OLT 402. The OLT 402controls the US data transmission formats and durations using a locallystored bandwidth map 504. The OLT 402 includes an elastic receiver 506that receives signal transmissions from the multiple ONUs 512 atspecified modulations on a symbol by symbol basis. Each ONU 512 mayinclude a scheduler 510 that receives scheduling information from theOLT 402 and controls an elastic transmitter 508 accordingly to transmitUS data. The scheduling information may include information aboutduration of time slot, value of guard time, and the modulation to beused on a symbol by symbol basis. The ONU 512 may also communicate withthe OLT 402 to inform the OLT 402 of its operational conditions such aspath loss being currently seen, its transmission/reception capabilitiesin terms of the types of modulation schemes supported and its upstreambandwidth requirements from time to time.

While in FIG. 4 and FIG. 5, each ONU is shown to have a single timeslot, in some embodiments, an ONU may be allocated multiple time slotsthat may be set apart from each other. Such may be the case, e.g., whenthe ONU has a need for very low latency data transmission and the ONUmay not tolerate waiting for an additional transmission frame.

FIG. 6 is a flowchart for a method 600 of optical communication. Themethod 600 includes receiving (602) bandwidth requests from multiplenetwork devices in an optical network, receiving (604) communicationcapability information of the multiple network devices, generating (606)a transmission schedule that specifies transmissions in the opticalnetwork in multiple time slots with a corresponding modulation format,and transmitting (608) and/or receiving data based on the transmissionschedule.

As described with respect to FIGS. 2 to 5, in some embodiments, themethod 600 may be implemented in an optical network in whichtransmissions are organized as transmission frames comprising a numberof time slots, where the transmission schedule specifies transmission inan integer number of transmission frames. For example, in someembodiments, one transmission schedule may be used per transmissionframe, while in some other embodiments, one transmission schedule may beused to specify transmissions in N (N is a positive integer greaterthan 1) transmission frames.

In some embodiments, the transmission schedule may be generated bydesignating a particular time slot for a downstream transmission to anetwork device (e.g., ONU), and selecting modulation formats for theparticular time slot based on the bandwidth requested by the networkdevice and communication capability of the network device. For example,the maximum modulation scheme supported by the network device may beused as an upper limit on the modulation format scheduled in thetransmission schedule. A similar transmission schedule may also begenerated for upstream transmissions.

The transmission capability of a device may be received during theprocess of registering the device when it enters the optical network.Alternatively or additionally, the communication capability informationmay be requested and/or received on a periodic basis during theoperation of the network.

FIG. 7 is a flowchart for a method 700 of optical communication. Themethod 700 includes transmitting (702) bandwidth requests to acontroller in an optical network, providing (704) communicationcapability information to the controller, receiving (706) a transmissionschedule that specifies transmissions in the optical network in multipletime slots with a corresponding modulation format, and transmittingand/or receiving (708) data based on the transmission schedule. Thecontroller may be, for example, the controller 204, which may beco-located with an OLT in the optical network or may be implemented onanother computer in the cloud. FIG. 8 shows an example of an opticalcommunication apparatus 800 comprising a memory 804, a processor 806, ascheduler 808, and an elastic transceiver 810. In some embodiments, thescheduler 808 may include a computational part that generates a scheduleand a storage part that stores information such as current bandwidthrequests, maximum modulation capability of each ONU, current bandwidthmap, and so on. The apparatus 800 may be configured to implement method600 and/or method 700.

It will be appreciated that techniques are disclosed for dynamicallyallocating bandwidth in a TDD optical network such that bandwidth use isoptimized in a two dimensional resource plane—one dimension beingtransmission time, and the other dimension being the modulation format.In addition, in some embodiments, a third dimension of optimization mayalso be used. This dimension may be a long term time average of theallocated bandwidth to a specific ONU, such that over a period of time,a given target average bandwidth is allocated to the ONU.

The disclosed and other embodiments, modules, and the functionaloperations described in this document can be implemented in digitalelectronic circuitry, or in computer software, firmware, or hardware,including the structures disclosed in this document and their structuralequivalents, or in combinations of one or more of them. The disclosedand other embodiments can be implemented as one or more computer programproducts, i.e., one or more modules of computer program instructionsencoded on a computer readable medium for execution by, or to controlthe operation of, data processing apparatus. The computer readablemedium can be a machine-readable storage device, a machine-readablestorage substrate, a memory device, a composition of matter effecting amachine-readable propagated signal, or a combination of one or morethem. The term “data processing apparatus” encompasses all apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them. A propagated signal is an artificially generated signal, e.g.,a machine-generated electrical, optical, or electromagnetic signal, thatis generated to encode information for transmission to suitable receiverapparatuses.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating an output. The processes and logic flows can also beperformed by, and an apparatus can also be implemented as, specialpurpose logic circuitry, e.g., an FPGA (field programmable gate array)or an ASIC (application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto optical disks; and CD ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of an invention that is claimed orof what may be claimed, but rather as descriptions of features specificto particular embodiments. Certain features that are described in thisdocument in the context of separate embodiments can also be implementedin combination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or a variation of a sub-combination. Similarly, whileoperations are depicted in the drawings in a particular order, thisshould not be understood as requiring that such operations be performedin the particular order shown or in sequential order, or that allillustrated operations be performed, to achieve desirable results.

Only a few examples and implementations are disclosed. Variations,modifications, and enhancements to the described examples andimplementations and other implementations can be made based on what isdisclosed.

What is claimed is:
 1. A method of optical communication, comprising:receiving bandwidth requests for a first transmission frame frommultiple network devices including a first network device in an opticalnetwork; receiving communication capability information about themultiple network devices including modulation capabilities for each ofthe multiple network devices including the first network device;generating a transmission schedule associating the first network devicewith one or more time slots and a modulation format, wherein a symbolrate and the modulation format are selected based on the receivedbandwidth request from the first network device and a modulationcapability of the first network device, wherein the symbol rate and themodulation format are dynamically selected for the first network devicefor each time slot, and wherein the other of the multiple networkdevices each have an assigned symbol rate and an assigned modulationformat dynamically selected according to each network device'smodulation capability and bandwidth request; and transmitting orreceiving data based on the transmission schedule.
 2. The method ofclaim 1, wherein the generating the transmission schedule includes:designating a particular time slot for a downstream transmission to thefirst network device; and selecting the modulation format for theparticular time slot based on the bandwidth requested by the firstnetwork device and the communication capability information about thefirst network device.
 3. The method of claim 1, further including:designating a particular time slot for an upstream transmission from thefirst network device; and selecting the modulation format for theparticular time slot based on the bandwidth requested by the firstnetwork device and the communication capability information about thefirst network device.
 4. The method of claim 1, wherein new bandwidthrequests are received for each transmission frame after the firsttransmission frame.
 5. The method of claim 1, wherein the receivedcommunication capability information including the modulationcapabilities apply to upstream and/or downstream modulationcapabilities.
 6. The method of claim 5, wherein the communicationcapability information for the first network device is received whileregistering the first network device with the optical network.
 7. Anoptical communication apparatus, comprising: a processor configured toreceive bandwidth requests for a first transmission frame from multiplenetwork devices including a first network device in an optical network;a receiver configured to receive communication capability informationabout the multiple network devices including modulation capabilities foreach of the multiple network devices including the first network device;a scheduler configured to generate a transmission schedule associatingthe first network device with one or more time slots and a modulationformat, wherein a symbol rate and the modulation format are selectedbased on the received bandwidth request from the first network deviceand a modulation capability of the first network device, wherein thesymbol rate and the modulation format are dynamically selected for thefirst network device for each time slot, and wherein the other of themultiple network devices each have an assigned symbol rate and anassigned modulation format dynamically selected according to eachnetwork device's modulation capability and bandwidth request; and atransceiver configured to transmit or receive data based on thetransmission schedule.
 8. The apparatus of claim 7, wherein thescheduler is configured to generate the transmission schedule by:designating a particular time slot for a downstream transmission to thefirst network device; and selecting the modulation format for theparticular time slot based on the bandwidth requested by the firstnetwork device and the communication capability information about thenetwork device.
 9. An optical communication apparatus comprising aprocessor configured to perform at least: receiving bandwidth requestsfor a first transmission frame from multiple network devices including afirst network device in an optical network; receiving communicationcapability information about the multiple network devices includingmodulation capabilities for each of the multiple network devicesincluding the first network device; generating a transmission scheduleassociating the first network device with one or more time slots and amodulation format, wherein a symbol rate and the modulation format areselected based on the received bandwidth request from the first networkdevice and a modulation capability of the first network device, whereinthe symbol rate and the modulation format are dynamically selected forthe first network device for each time slot, and wherein the other ofthe multiple network devices each have an assigned symbol rate and anassigned modulation format dynamically selected according to eachnetwork device's modulation capability and bandwidth request; andtransmitting or receiving data based on the transmission schedule. 10.The apparatus of claim 9, wherein the receiving the transmissionschedule includes: receiving information that a particular time slot isdesignated for a downstream transmission; and operating an opticalreceiver using the modulation format for the particular time slot toreceive a transmission during the particular time slot.
 11. A computerprogram product comprising a computer readable medium having code storedthereupon, the code, when executed by a processor, causing the processorto perform: receiving bandwidth requests for a first transmission framefrom multiple network devices including a first network device in anoptical network; receiving communication capability information aboutthe multiple network devices including modulation capabilities for eachof the multiple network devices including the first network device;generating a transmission schedule associating the first network devicewith one or more time slots and a modulation format, wherein a symbolrate and the modulation format are selected based on the receivedbandwidth request from the first network device and a modulationcapability of the first network device, wherein the symbol rate and themodulation format are dynamically selected for the first network devicefor each time slot, and wherein the other of the multiple networkdevices each have an assigned symbol rate and an assigned modulationformat dynamically selected according to each network device'smodulation capability and bandwidth request; and transmitting orreceiving data based on the transmission schedule.
 12. The computerprogram product of claim 11, wherein the code further causes theprocessor to perform: designating a particular time slot for an upstreamtransmission from a network device; and selecting the modulation formatfor the particular time slot based on the bandwidth requested by thenetwork device and/or the communication capability information about thenetwork device.